Final answer:
The subject of the question appears to be a mix-up with the name Nelly Sachs; the individual described actually began publishing children's poems at the age of twelve through a magazine, although he is not Nelly Sachs.
Step-by-step explanation:
Nelly Sachs began writing poems at a young age. From the information provided, it seems there may be confusion with the name Nelly Sachs, who is a different poet than the one described.
Assuming the student is inquiring about the person described, who is not Nelly Sachs, his interest in writing was evident in his youth, and he began publishing his works at the age of twelve. Through a mimeographed magazine titled New Myong-dong, he shared his children's poems, which he wrote with the assistance of his childhood friend and cousin, Song Mong-kyu.